There is a plurality of different applications for free-cutting steels. Examples of applications are in measuring probes and instruments, as automotive parts (such as fuel injection systems and precision valves for ABS brakes) and as watch parts, which are all examples of applications manufactured from and/or using wires. The applications mentioned all utilize wire or rod in small dimensions. This may also lead to a necessity of using low cutting speeds during manufacturing of a component due to limitations in the machining equipment used. In this context, small dimensions are considered to be wire diameters less than 15 mm. The applications mentioned above generally require the properties machinability, hardenability and wear resistance to be concurrently optimised. In some cases, also the corrosion properties, i.e. tendency to formation of rust, during storage and/or manufacturing of a component of the steel might be of importance.
Free-cutting steels commonly used today often contain lead, which is an effective element for providing the desired machinability. However, lead is a hazardous element for the environment and therefore the development within environmental legislation indicates that lead may become prohibited or limited as alloying material in steel. In this context, environmentally friendly is considered to mean non hazardous for nature or persons in close proximity with the material, during manufacturing, especially hot working, machining of components, use and recycling.
One example of a lead containing free-cutting steel is Sandvik 20AP, which has a nominal composition of 1% by weight of C, 0.2% by weight of Si, 0.4% by weight of Mn, 0.05% by weight of S and 0.2% by weight of Pb. This steel has very good machinability, wear resistance and hardenability as well as excellent dimensional stability after heat treatment. Due to these properties, it is highly suitable for long narrow components, such as shafts in measuring instruments, and precision valves, especially in the automotive industry. It can also be used in other applications such as watch components, measuring probes and precision tools. However, since this material contains lead it is not considered as environmentally friendly.
Examples of lead free free-cutting steels can be found in US 2003/0113223 A1, EP 1270757 A and U.S. Pat. No. 5,648,044 A, all which are for machine structural use. These steels do, however, not provide properties that are satisfactory for small dimensions, and do therefore not constitute appropriate compositions.
Consequently, it is an object of the invention to provide an alternative steel, which may be used as wire, especially in small dimensions, and which is not detrimental to the environment.